1. Field of the Invention
This invention relates to an apparatus that may be used in wells during drilling operations. More particularly, a valve having a full-opening bore that may be placed in a tubular such as casing and operated mechanically to isolate pressure when it is closed is provided.
2. Description of Related Art
Drilling of wells in an underbalanced or balanced pressure condition has well-known advantages. In this condition, pressure in the formation being drilled is equal to or greater than pressure in the wellbore. When there is a need to withdraw the drill pipe from the well, pressure in the wellbore must be controlled to prevent influx of fluids from a formation into the wellbore. The usual remedy of preventing influx of fluid from a formation—by increasing fluid density in the wellbore—may negate the advantages of balanced or underbalanced drilling. Therefore, downhole valves have been developed to isolate fluid pressure below the valve. They have been variously called “Downhole Deployment Valves” (DDV) or “Downhole Isolation Valves” (DIV). Technical literature includes reports of the usage of such valves in Under-Balanced Drilling (UBD) For example, SPE 77240-MS, “Downhole Deployment Valve Addresses Problems Associated with Tripping Drill Pipe During Underbalanced Drilling Operations,” S. Herbal et al, 2002, described uses of such valves in industry. The DDV or DIV as a tool in the broad area of “Managed Pressure Drilling” can be generally surmised from the survey lecture “Managed Pressure Drilling,” by D. Hannagan, SPE 112803, 2007. There it is listed under “Other Tools” and called a “Downhole Casing Isolation Valve” (DCIV) or “Downhole Deployment Valve.” Services and products for providing Managed Pressure Drilling have been commercialized by AtBalance of Houston, Tex., Weatherford International, Inc. of Houston, Tex. and other companies.
A DCIV is placed in a casing at a selected depth, considering conditions that may be encountered in drilling the well. The valve is normally placed in an intermediate casing string, and the effective Outside Diameter (OD) of the valve is limited by the Inside Diameter (ID) of the surface casing through which it must pass. For example, in 9⅝-inch intermediate casing, the valve preferably will be full-opening (have a bore at least equal to the ID of the 9⅝ inch casing, about 8.681 inches, or at least be as large as the drill bit to be used) and must pass through the drift diameter of the surface casing, which may be 10.5 inches. Therefore, the valve must be designed to severely limit the thickness of the valve body while being large enough for a bit to pass through.
A DCIV is disclosed in U.S. Pat. No. 6,209,663. A flapper valve is illustrated, but other types of valves, such as ball valves or other rotary valves are disclosed. The valves may be mechanically operated or operated by biasing means (e.g., springs). U.S. Pat. No. 6,167,974 discloses a flapper-type DCIV valve that is operated by a shifting device that is carried on a drill bit and deposited in the valve when the drill string is tripped out of the well.
Prior art valves relying on a flapper mechanism have been commercially successful, but improvements in reliability and absence of leakage are needed. A rotary valve having minimum difference between outside diameter and inside diameter is needed. The ability of the valve to seal with differential pressure in two directions is also preferred.
It should be understood that valves designed for downhole isolation may also be used for a variety of purposes. In wells, there may be a need to open or close a valve to control pressure near the bottom of the well when the hydrostatic pressure of fluid in the well is higher than desired, or there may be a need to isolate pressure in a well bore drilled from another well bore. In industry, valves requiring a minimum of wall thickness between the interior passage through the valve and the exterior surface of the valve may be needed for a variety of applications in any industry utilizing mechanical techniques.